1. Field of the Invention
The present invention relates to a heat treatment apparatus of a light-emission type for exposing a substrate including a semiconductor wafer, a glass substrate and the like received within a process chamber to a flash of light to heat the substrate, and a method of cleaning the heat treatment apparatus of the light-emission type.
2. Description of the Background Art
As is well known in the art, semiconductor parts are manufactured after passing through a multiplicity of process steps, and various manufacturing apparatuses corresponding to the respective process steps are employed for the manufacture. Many of the apparatuses are each provided with a cleaning mechanism therein because the manufacture of the semiconductor parts and the like becoming finer necessitates an ultraclean atmosphere. For example, Japanese Patent Application Laid-Open No. 7-321046 (1995) discloses a technique for removing organic materials on a substrate by passing an ozone gas under ultraviolet irradiation. Also, Japanese Patent Application Laid-Open No. 9-17705 (1997) discloses a technique for cleaning away undesired films deposited on the inner wall surfaces of a process chamber and the surfaces of a structure inside the process chamber at about 200° C. while feeding a ClF3 gas thereto. Further, Japanese Patent Application Laid-Open No. 7-230954 (1995) discloses a cleaning technique which heats residues deposited on the surfaces of a structural component inside a chamber to decompose and remove the residues in a plasma processing apparatus.
One of the steps for manufacturing semiconductor parts and the like includes an ion implantation step for implanting ions of boron, arsenic and the like into a silicon wafer. A heating process is performed for the purpose of activating the ions implanted in the semiconductor wafer. The heating process for the activation of the ions is carried out by heating (or annealing) the semiconductor wafer to a temperature of, for example, about 1000° C. to about 1100° C. For this process, a lamp annealer has been conventionally used which utilizes the energy of light emitted from a halogen lamp to raise the temperature of the wafer at a rate of about hundreds of degrees per second.
It has turned out, however, that even the execution of the process of activating the ions implanted in the semiconductor wafer by the use of a heat treatment apparatus which employs a halogen lamp to raise the temperature of the semiconductor wafer at a rate of about hundreds of degrees per second causes a phenomenon in which the ions implanted in the semiconductor wafer exhibit a round or dull profile, i.e., the ions are diffused by heat. The occurrence of such a phenomenon has created a problem such that more ions than necessary must be implanted because the implanted ions are diffused if the ions are implanted even at a high concentration into the surface of the semiconductor wafer.
To solve the above-mentioned ion diffusion problem, for example, Japanese Patent Application Laid-Open No. 59-169125 (1984) and Japanese Patent Application Laid-Open No. 63-166219 (1988) have proposed a technique of exposing the surface of a semiconductor wafer to a flash of light from a xenon flash lamp or the like to raise the temperature of only the surface of the semiconductor wafer implanted with ions in an extremely short time (several milliseconds or less). Because there is not enough time for the ions to diffuse, the temperature rise in such an extremely short time by the use of the xenon flash lamp allows only the activation of the ions without providing the round or dull profile of the ions implanted in the semiconductor wafer.
In such a flash lamp annealer, there are cases where the breakage of a semiconductor wafer occurs due to the momentary exposure of the semiconductor wafer to light having enormous energy during flash heating. If a semiconductor wafer is cracked and broken, a large amount of particles resulting from the broken pieces of the semiconductor wafer itself and damages to a peripheral structure are produced in a chamber. When the breakage of a semiconductor wafer occurs, the chamber is opened, of course, for maintenance including collecting the broken pieces. It is, however, quite difficult to completely remove the produced particles. Further, opening the chamber causes new external particles to enter the chamber. If the flash heating process is performed while particles remain in the chamber, the particles adhere to the semiconductor wafer to result in a processing failure.
To prevent this, a technique has been conventionally adopted which performs flash heating upon dummy wafers after the maintenance is performed with the chamber opened, to cause the particles to adhere to the dummy wafers, thereby removing the particles. However, the removal of the particles remaining in the chamber to an acceptable level or lower requires a substantial number of dummy wafers and a substantial amount of time, resulting in a significant increase in cost.